JP4870051B2 - FIXING DEVICE, IMAGE FORMING DEVICE, FIXING DEVICE CONTROL METHOD, FIXING DEVICE CONTROL PROGRAM, AND RECORDING MEDIUM THEREOF - Google Patents

Description

  The present invention relates to an external belt heating type fixing device used in an electrophotographic image forming apparatus and an image forming apparatus including the fixing device.

  As a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, a heat roller fixing type fixing device is frequently used. A fixing device of a heat roller fixing system includes a pair of rollers (fixing roller and pressure roller) that are in pressure contact with each other, and the roller is heated by heating means including a halogen heater or the like disposed in both or one of the roller pairs. After the pair is heated to a predetermined temperature (fixing temperature), the recording paper on which the unfixed toner image is formed is fed to the pressure contact part (fixing nip part) of the roller pair, and the heat and pressure are passed through the pressure contact part. Thus, the toner image is fixed.

  By the way, in a fixing device provided in a color image forming apparatus, it is common to use an elastic roller provided with an elastic layer made of silicon rubber or the like on the surface of the fixing roller. By using an elastic roller as the fixing roller, the surface of the fixing roller is elastically deformed according to the unevenness of the unfixed toner image and comes into contact so as to cover the toner image surface. It is possible to perform heat fixing on an unfixed toner image satisfactorily. Further, due to the effect of releasing the distortion of the elastic layer at the fixing nip, it is possible to improve the releasability for color toners that are more likely to be offset than in monochrome. Furthermore, since the nip shape of the fixing nip portion is convex upward (on the fixing roller side) (so-called reverse nip shape), it is possible to improve the paper peeling performance without using a peeling means such as a peeling claw. Paper can be peeled off (self-stripping), and image defects caused by the peeling means can be eliminated.

  However, in a fixing roller having an elastic layer, the heat conductivity of the elastic layer is very low. Therefore, when a heating means is provided inside the fixing roller, the heat transfer efficiency is lowered and the warm-up time is increased. When the speed is increased, there is a problem that the fixing roller temperature does not follow.

  In order to solve such a problem, a technique (external heating fixing method) is known in which an external heating belt is brought into contact with the surface of the fixing roller and the fixing roller is heated from the outside as disclosed in Patent Document 1. Yes. That is, in the external heating fixing method, an external heating belt heated to a temperature higher than that of the heated roller is brought into contact with the surface of the fixing roller or pressure roller, and the heated roller is heated from the surface. Heating performance is greatly improved by the contact of the external heating belt.

  Further, Patent Document 1 includes a contact / separation mechanism that separates the external heating belt from the fixing roller, and separates the external heating belt from the fixing roll in the case of cleaning jamming or toner adhering to the belt. Is described.

Furthermore, in Patent Document 2, in order to prevent the toner from transferring from the fixing roller to the external heating body and being fixed and deposited on the external heating body such as a roll or a belt, the surface of the fixing roller is prevented from being damaged. In the warm-up or standby mode, when the external heating body and the fixing roller reach a reference temperature equal to or higher than the softening point of the toner, the external heating body is pressed against the fixing roller.
JP 2004-198659 A (publication date: July 15, 2004) Japanese Patent No. 3632724 (publication date: January 29, 1999)

  However, in the above conventional technique, when a belt is used as the external heating body, no consideration is given to the tension acting on the belt in a state where the rotation of the belt is stopped or the belt is separated from the fixing roller. For this reason, in the above conventional technique, if the belt is stopped and the belt is kept in tension for a long time, the belt has a die (curl) according to the shape when left unattended. Depending on the mold, there is a problem that a rotation failure such as an increase in driving torque or slip occurs at the start of rotation.

  If the belt does not rotate or rotates at a speed slower than the original rotational speed, the heat supply capacity from the belt to the heated roller is reduced, and it is difficult to maintain the heated roller at a predetermined temperature. Therefore, fixing performance cannot be secured due to low temperature offset. In addition, since the heat supply from the belt is dominant in the heating of the heated roller, when the heated roller starts heating from a relatively low temperature, such as during warm-up, it is sufficient that the belt slips. If the amount of heat cannot be supplied, the warm-up time becomes longer and the transition time between jobs becomes longer, so that the original performance cannot be exhibited.

  In addition, when the rotation failure of the belt occurs, the surface of the heated roller and the surface of the belt are rubbed, and the surface of the fixing roller is damaged by toner accumulated due to offset or the like on the surface of the heated roller or the belt.

  In general, in order to heat the heated roller quickly and with good controllability, a belt having a small heat capacity is used, and a heat source for heating the belt has a large heat supply amount. For this reason, if the belt does not rotate properly and a sufficient amount of heat cannot be supplied to the heated roller, the belt will be overheated even if the power supply to the heat source is cut off, and the belt, belt support roller, bearing, etc. In some cases, peripheral components may be damaged, or an excessive temperature rise prevention element (such as a thermostat or a temperature fuse) that does not need to operate may malfunction, causing unnecessary trouble.

  In addition, from the viewpoint of releasability, a material having a low frictional resistance such as PFA tube, PTFE, PFA coating or the like is often used for the fixing member and the surface layer of the belt. Defects are particularly likely to occur.

  Also, on the surface of the belt, which is an external heating body, the toner is transferred from the fixing roller as the heated roller due to various conditions such as the physical properties of the toner, release conditions, and temperature conditions, and the nip between the belt and the fixing roller. There may be cases where sticking matter or deposits such as toner are present in the portion (heating nip portion). Then, when the fixing roller is driven to rotate with a solid matter or deposit such as toner interposed in the nip, the toner softened by heat functions like a lubricating oil, and transmits the driving force from the fixing roller to the belt. Since it will inhibit, it will become easy to produce a slip especially.

  The present invention has been made in view of the above-described conventional problems. The object of the present invention is to heat a heated member and bring the belt into contact with a heated member to be rotated. In the fixing device that is driven to rotate by the heating member, it is intended to suppress the rotation failure of the belt.

  In order to solve the above-described problems, the fixing device of the present invention is configured to rotate and drive at least one of the fixing member and the pressure member that are in contact with each other with a predetermined load, and the fixing member and the pressure member. Rotation driving means for rotating the fixing member and the pressure member, and a belt stretched on a plurality of support members are heated by the heating means and brought into contact with the peripheral surface of the fixing member to heat the fixing member. And an external heating device that causes the belt to be driven and rotated by the fixing member, and the recording material carried into the contact portion between the fixing member and the pressure member is sandwiched between the fixing member and the pressure member. A fixing device that fixes an unfixed image on the recording material to the recording material by heat of the peripheral surface of the fixing member by being conveyed while the belt is being relaxed. A tension changing means for performing a tension changing operation including at least one tension applying operation for increasing the tension of the belt more than a tension at the time of the relaxing operation; and a control means for controlling the operation of the tension changing means. The control means performs the tension changing operation on the tension changing means after the heating means starts heating the belt and before the recording material is carried between the fixing member and the pressure member. It is characterized by having it be done.

  According to said structure, the tension | tensile_strength fluctuation | variation which performs the tension | tensile_strength fluctuation | variation operation | movement which includes the tension | tensile_strength operation | movement which makes the tension | tensile_strength of the said belt small, and the tension | tensile_strength provision operation | movement which makes the tension | tensile_strength of the said belt larger than the tension | tensile_strength at the said loosening operation | Means and control means for controlling the operation of the tension fluctuation means. The control means causes the tension changing means to perform a tension changing operation after the heating means starts heating the belt and before the recording material is carried between the fixing member and the pressure member. Thus, by heating the belt and changing the tension of the belt, the shape of the belt can be changed, and the mold (curl) attached to the belt can be relaxed. As a result, it is possible to suppress a rotation failure such as an increase in driving torque or slip between the fixing member and the die attached to the belt. As a result, the warm-up time can be shortened, and a fixing failure (image failure) due to an insufficient heat supply amount to the fixing member can be prevented.

  The rotation driving operation by the rotation driving means is performed after the heating start of the belt, and the control means starts heating the belt by the heating means and then rotates the rotation driving means. Before starting the rotational driving operation according to the above, the tension varying means may be configured to perform the tension varying operation.

  According to the above configuration, the belt mold can be relaxed before the rotation of the fixing member and the belt is started. Therefore, it is possible to suppress the occurrence of defective rotation of the belt when the rotation driving operation of the fixing member is started. Therefore, it is possible to prevent the rotation driving means from being overloaded due to an increase in the driving torque accompanying the belt rotation failure, and the belt and the fixing member from being damaged by the belt slip.

  In addition, first temperature detection means for detecting the temperature of the belt is provided, and the control means sets the detected temperature of the belt by the first temperature detection means to be equal to or higher than a temperature at which the residual stress of the belt starts to be relaxed. When the first temperature is reached, the tension changing means may perform the tension changing operation.

  According to the above configuration, the tension fluctuation operation is performed when the temperature of the belt reaches or exceeds the temperature at which the residual stress of the belt starts to be relaxed. In this way, the mold attached to the belt can be more effectively relaxed by changing the tension after heating to a temperature at which the residual stress of the belt is relaxed or higher.

  Further, the control means performs the rotational driving operation by the rotational driving means when the detected temperature of the belt by the first temperature detecting means reaches a second temperature set to a temperature higher than the first temperature. It may be configured to start.

  According to the above configuration, the belt mold can be relaxed before the rotation of the fixing member and the belt is started. Therefore, it is possible to suppress the occurrence of defective rotation of the belt when the rotation driving operation of the fixing member is started. Therefore, it is possible to prevent the rotation driving means from being overloaded due to an increase in the driving torque accompanying the belt rotation failure, and the belt and the fixing member from being damaged by the belt slip.

  Further, the control means determines whether or not rotation failure has occurred in the belt after starting the rotation drive operation by the rotation drive means, and if the rotation failure has occurred, It is good also as a structure which performs tension | tensile_strength fluctuation | variation operation | movement.

  According to said structure, after starting rotation drive operation by a rotation drive means, when the rotation defect has arisen in the belt, tension fluctuation | variation operation | movement can be performed. As a result, the mold attached to the belt can be relaxed and rotation failure can be suppressed. Further, even if the belt has a rotation failure, the contact area between the belt and the fixing member changes if the belt rotates. Therefore, even when there is a fixed matter / deposit such as toner on the surface of the belt or the fixing member, it is possible to prevent a rotation failure such as a slip due to the fixed matter / deposit.

  Further, the control means sets the detected temperature of the belt by the first temperature detecting means to a temperature lower than the second temperature within a predetermined time after starting the rotational driving operation by the rotational driving means. When the temperature does not fall below the threshold temperature, the tension changing means may be configured to perform the tension changing operation.

  According to the above configuration, it is possible to determine whether or not the rotation failure of the belt has occurred based on whether or not the belt temperature falls below the threshold temperature within a predetermined time after the rotation driving operation is started. That is, after the rotation driving operation is started, when the belt is appropriately driven and rotated, the amount of heat transferred from the belt to the fixing member increases, so the temperature of the belt once decreases, and then the heating means Heating raises the belt temperature again. Therefore, the predetermined time is set to the time when the belt temperature starts to rise again (or a time close to this time), and the threshold temperature is set to the temperature when the belt temperature starts to rise again (or a temperature close to this temperature). By doing so, it can be determined whether or not the belt is rotating properly, that is, whether or not a rotation failure has occurred. Then, if the belt temperature does not drop below the threshold temperature within a predetermined time after starting the rotation driving operation, that is, if the belt rotation failure occurs, the belt rotation failure is performed by performing the tension fluctuation operation. The fixing member can be appropriately driven and rotated.

  The fixing device according to the present invention rotates the at least one of the fixing member and the pressure member that are in contact with each other with a predetermined load, and the fixing member and the pressure member. A rotation driving means for rotating and a belt stretched on a plurality of support members are heated by a heating means and brought into contact with the peripheral surface of the fixing member to heat the fixing member and to fix the belt to the fixing member. An external heating device that is driven to rotate, and the recording material carried into the contact portion between the fixing member and the pressure member is conveyed while being sandwiched between the fixing member and the pressure member. A fixing device for fixing an unfixed image on a material to the recording material by heat of a peripheral surface of the fixing member, a relaxation operation for reducing the tension of the belt, and a tension during the relaxation operation A tension changing means for performing a tension changing operation including at least one tension applying operation for increasing the tension of the belt, a control means for controlling the operation of the tension changing means, and a first means for detecting the temperature of the belt. At least one temperature detecting means selected from the group consisting of a first temperature detecting means, a second detecting means for detecting the temperature of the fixing member, and a third temperature detecting means for detecting the temperature of the pressure member. The means starts the heating of the belt by the heating means only when the temperature detected by each temperature detecting means is lower than a predetermined temperature preset for each temperature detecting means, and then uses the rotation driving means. A configuration may be adopted in which the tension changing means is caused to perform the tension changing operation before starting the rotation driving operation. Note that the predetermined temperature has passed a predetermined time set to a time when the belt does not form even if the belt is left heated and rotated after the last heating and rotation of the belt and then the heating is not performed. It is preferable to set the temperature of the fixing member, the pressure member, and the belt at the time.

  According to said structure, the tension | tensile_strength fluctuation | variation which performs the tension | tensile_strength fluctuation | variation operation | movement which includes the tension | tensile_strength operation | movement which makes the tension | tensile_strength of the said belt small, and the tension | tensile_strength provision operation | movement which makes the tension | tensile_strength of the said belt larger than the tension | tensile_strength at the said loosening operation | Means and control means for controlling the operation of the tension fluctuation means. Further, at least one of the first temperature detecting means for detecting the temperature of the belt, the second detecting means for detecting the temperature of the fixing member, and the third temperature detecting means for detecting the temperature of the pressure member is detected. Means. Then, the control means starts the heating of the belt by the heating means only when the temperature detected by each temperature detection means is lower than the predetermined temperature preset for each temperature detection means, and then the rotational drive by the rotational drive means Before starting the operation, the tension changing means is caused to perform the tension changing operation.

  As a result, when the temperature detected by each temperature detecting means is lower than a predetermined temperature preset for each temperature detecting means, the belt is heated and the tension of the belt is changed to change the shape of the belt. Can relax the mold attached to the belt. As a result, it is possible to suppress a rotation failure such as an increase in driving torque or slip between the fixing member and the die attached to the belt. On the other hand, if the temperature detected by any one of the temperature detection means is equal to or higher than a predetermined temperature preset for each temperature detection means, there is a low possibility that a rotation failure of the belt due to the mold attached to the belt will occur. Do not drive. Thereby, unnecessary operations can be omitted, the warm-up time can be shortened, and the power consumption can be reduced.

  Further, the control means may be configured to perform the relaxation operation and the tension applying operation a plurality of times as the tension fluctuation operation.

  According to said structure, relaxation of the type | mold attached to the belt can be accelerated | stimulated and the rotation failure of the belt by the type | mold attached to the belt can be suppressed more effectively.

  The image forming apparatus of the present invention includes any one of the fixing devices described above. Accordingly, rotation failure such as an increase in driving torque or slip between the belt and the fixing member due to the mold attached to the belt can be suppressed, so that the warm-up time of the fixing device can be shortened and the fixing member can be shortened. It is possible to prevent a fixing failure (image failure) due to a shortage of heat supply to the printer.

  In order to solve the above-described problem, the fixing device control method of the present invention rotationally drives at least one of the fixing member and the pressure member that are in contact with each other with a predetermined load, and the fixing member and the pressure member. The fixing member and the pressure member are rotated by the rotation driving means, and the belt stretched on the plurality of supporting members is heated by the heating means and brought into contact with the peripheral surface of the fixing member. An external heating device that heats the member and rotates the belt following the fixing member, and the recording material carried into the contact portion between the fixing member and the pressure member is the fixing member and the pressure member. And fixing the unfixed image on the recording material onto the recording material by the heat of the peripheral surface of the fixing member, the fixing device comprising: A tension varying means for performing a tension varying operation including at least one of a relaxing operation for reducing the tension of the belt and a tension applying operation for increasing the tension of the belt more than a tension at the time of the relaxing operation, Including a step of causing the tension changing means to perform the tension changing operation after the heating means starts heating the belt and before the recording material is carried between the fixing member and the pressure member. It is a feature.

  According to the above method, after starting the heating of the belt by the heating means, the tension changing means performs the tension changing operation before the recording material is carried between the fixing member and the pressure member. Thus, by heating the belt and changing the tension of the belt, the shape of the belt can be changed, and the mold attached to the belt can be relaxed. As a result, it is possible to suppress a rotation failure such as an increase in driving torque or slip between the fixing member and the die attached to the belt. As a result, the warm-up time can be shortened, and a fixing failure (image failure) due to an insufficient heat supply amount to the fixing member can be prevented.

  The fixing device may be realized by a computer. In this case, by causing the computer to operate as the control means, a program for realizing the fixing device by the computer, and a computer readable recording the same Such recording media are also included in the scope of the present invention.

  As described above, the fixing device according to the present invention includes a tension fluctuation that includes a relaxation operation for reducing the tension of the belt and a tension applying operation for increasing the tension of the belt more than once during the relaxation operation. Tension changing means for performing the operation, and control means for controlling the operation of the tension changing means. The control means starts heating the belt by the heating means, and then the fixing member, the pressure member, Before the recording material is carried in, the tension changing means is caused to perform the tension changing operation.

  Therefore, the mold attached to the belt can be relaxed, and rotation failure such as an increase in driving torque or slip between the fixing member and the mold attached to the belt can be suppressed.

Embodiment 1
An embodiment of the present invention will be described.

  FIG. 2 is a cross-sectional view illustrating a schematic configuration of a color image forming apparatus (image forming apparatus) according to the present embodiment.

  As shown in this figure, this color image forming apparatus is a so-called so-called so-called four-color visible image forming unit 40 (40Y, 40M, 40C, 40B) arranged along a transport path of recording paper P (material to be heated). It is a tandem printer. Specifically, the recording paper conveyance means 50 that conveys the recording paper P along a conveyance path connecting the supply tray 55 of the recording paper P and the fixing device 1, and four sets of the recording paper P arranged along the conveyance path. Visible image forming units 40Y, 40M, 40C, and 40B are provided. Then, the respective color toners are multiplex-transferred by the visible image forming units 40Y, 40M, 40C, and 40B onto the recording paper P that is transported along the transport path by the recording paper transporting unit 50, and then the toner is transferred by the fixing device 1. A full color image is formed by being fixed on the recording paper P.

  The recording paper transport means 50 includes a driving roller 51, an idling roller 52, and an endless transport belt 53 stretched between these rollers. Further, by rotating the driving roller 51 by a driving means (not shown), the conveying belt 53 is rotated along the conveying path at a predetermined peripheral speed (355 mm / s in this embodiment), and electrostatically is transferred onto the conveying belt 53. The adsorbed recording paper P is conveyed.

  Each visible image forming unit 40 includes a charging roller 42, a laser beam irradiation unit 43, a developing device 44, a transfer roller 45, and a cleaner 46 around the photosensitive drum 41. The developing devices 44 of the visible image forming units 40Y, 40M, 40C, and 40B contain yellow (Y), magenta (M), cyan (C), and black (B) toners, respectively. Each visible image forming unit 40 forms a toner image on the recording paper P by the following steps.

  That is, after the surface of the photosensitive drum 41 is uniformly charged by the charging roller 42, the surface of the photosensitive drum 41 is laser-exposed by the laser light irradiation unit 43 in accordance with image information to form an electrostatic latent image. Thereafter, the electrostatic latent image on the photosensitive drum 41 is developed by the developing unit 44 to make the toner image visible, and the transferred toner image is applied with a bias voltage having a polarity opposite to that of the toner. 45 is sequentially transferred onto the recording paper P conveyed by the recording paper conveying means 50. Thereafter, the recording paper P to which the toner images of the respective colors are transferred is peeled off from the transport belt 53 by the curvature of the drive roller 51 and then transported to the fixing device 1. Then, an appropriate temperature and pressure are given by the fixing device 1. As a result, the toner dissolves and is fixed (fixed) on the recording paper P to form a robust image.

  Next, the configuration of the fixing device 1 will be described. FIG. 1 is a schematic diagram illustrating a configuration of the fixing device 1. The fixing device 1 fixes an unfixed toner image formed on the surface of a recording paper (recording material) on the recording paper with heat and pressure. The unfixed toner image may be a developer such as a non-magnetic one-component developer (non-magnetic toner), a non-magnetic two-component developer (non-magnetic toner and carrier), or a magnetic developer (magnetic toner). Toner).

  As shown in FIG. 1, the fixing device 1 includes a fixing roller (fixing member) 60, a pressure roller (pressure member) 70, an endless belt (external heating belt) 83 as an external heating member, and an endless belt 83. Are heating rollers 81 and 82 for suspending and heating, heater lamps (heating means) 86 and 87 which are heat sources for heating the heating rollers 81 and 82, and a heat source for heating the fixing roller 60, respectively. Heater lamps 64a and 64b, a heater lamp 74 that is a heat source for heating the pressure roller 70, and temperatures constituting temperature detection means for detecting the temperatures of the fixing roller 60, the pressure roller 70, and the endless belt 83 Thermistors 65, 75, and 85 as sensors and a web cleaning device 95 for cleaning the fixing roller 60 are provided. Further, the thermistor 65 detects the temperature at the center portion in the longitudinal direction and the temperature at the end portion of the fixing roller 60. The endless belt 83, the heating rollers 81 and 82, and the heater lamps 86 and 87 are provided in an external heating device 80 described later. As the heater lamps 64a, 64b, 74, 86, 87, heater lamps (halogen lamps) having the same heating width with a rated power of 475 W were used.

  In this embodiment, the heater lamps have the same rated power, but the present invention is not limited to this, and various combinations are possible. For example, the heater lamp 64a may be 550W, the heater lamp 64b may be 400W, the heater lamp 74 may be 450W, and the heater lamps 86 and 87 may be 475W. As another example, the heater lamps 64a, 74, 86, and 87 are 550W and the heater The lamp 64b may be 400W.

  The fixing roller 60 and the pressure roller 70 are pressed against each other with a predetermined load (for example, 600 N in the present embodiment), and the fixing nip portion N (the fixing roller 60 and the pressure roller 70 contact each other). Part of contact). In this embodiment, the nip width (the width of the fixing nip portion N in the recording paper conveyance direction) is 8 mm. By feeding a recording sheet on which an unfixed toner image is formed in the fixing nip N and passing the fixing nip N, the toner image is fixed on the recording sheet. When the recording paper passes through the fixing nip N, the fixing roller 60 contacts the toner image forming surface of the recording paper, while the pressure roller 70 contacts the surface of the recording paper opposite to the toner image forming surface. It has become.

  The fixing roller 60 is for heating a recording sheet on which an unfixed toner image passing through the fixing nip N is formed by being heated to a predetermined temperature (200 ° C. in the present embodiment). The fixing roller 60 has a three-layer structure in which a core metal 61, an elastic layer 62, and a release layer 63 are formed in this order from the inside. For the metal core 61, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof is used. Silicone rubber is suitable for the elastic layer 62, and fluorine resin such as PFA (a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) is suitable for the release layer 63. In this embodiment, as the fixing roller 60, an aluminum cored bar coated with a 2 mm thick silicon rubber layer and further coated with a 40 μm thick PFA tube is used.

  In the fixing roller 60, two heater lamps 64a and 64b for heating the fixing roller 60 are arranged in the longitudinal direction of the fixing roller 60. One is a heater lamp that heats the central portion, and the other is a heater lamp that heats both ends. When the control device 90 supplies (energizes) power to each of these heater lamps from a power supply circuit (not shown), the heater lamps emit light and infrared rays are emitted from the heater lamps. As a result, the inner peripheral surface of the cored bar of the fixing roller 60 is heated by absorbing infrared rays, and the entire fixing roller is heated.

  Similar to the fixing roller 60, the pressure roller 70 also has an elastic layer 72 made of silicon rubber or the like on the outer peripheral surface of a cored bar 71 made of steel, stainless steel, aluminum, or the like, and further a release layer 73 such as PFA. Is formed. A heater lamp 74 that heats the pressure roller 70 is disposed inside the pressure roller 70. Similar to the fixing roller 60, the entire pressure roller 70 is heated by the heater lamp 74.

  The endless belt 83 is in contact with the surface of the fixing roller 60 while being heated to a predetermined temperature (220 ° C. in the present embodiment), and heats the surface of the fixing roller 60. The endless belt 83 is suspended by two heating rollers 81 and 82. In addition, heater lamps 86 and 87 as heating means for heating the heating rollers 81 and 82 are disposed inside the heating rollers 81 and 82. When the control device 90 supplies power to the heater lamps 86 and 87 from a power supply circuit (not shown), the heater lamps 86 and 87 emit light and radiate infrared rays. Thereby, the inner peripheral surface of the cored bar of the heating rollers 81 and 82 is heated by absorbing infrared rays, and the endless belt 83 is indirectly heated via the heating rollers 81 and 82.

  In this embodiment, the outer diameter of the fixing roller 60 is φ60 mm, the outer diameter of the heating rollers 81 and 82 is φ14.8 mm, and the distance between the two heating rollers 81 and 82 is 38.55 mm. In this embodiment, two heating rollers are provided. However, the present invention is not limited to this, and the endless belt 83 may be stretched around three or more heating rollers.

  The endless belt 83 is provided on the upstream side of the fixing nip portion N with respect to the rotation direction of the fixing roller 60, and is pressed against the fixing roller 60 with a predetermined pressing force (40N in this embodiment). A mechanism (configuration of the external heating device 80) for pressing the endless belt 83 against the fixing roller 60 will be described later. A heating nip (a portion where the fixing roller 60 and the endless belt 83 abut each other) is formed between the fixing roller 60 and the heating roller. The endless belt 83 is rotated by the fixing roller 60 when the fixing roller 60 is rotated, and the heating rollers 81 and 82 are also rotated by the rotation of the endless belt 83. . Note that the heating nip width of the heating nip portion (the width of the heating nip portion in the fixing roller rotation direction) is such that the endless belt 83 can appropriately heat the fixing roller 60, and the endless belt 83 is appropriately set to the fixing roller 60. It is set so that it can be driven to rotate. In this embodiment, the heating nip width is 20 mm.

  As the endless belt 83, a 90 μm thick polyimide (Ube Industries, trade name: Upilex S) base material surface coated with a fluorine resin blended with PFTE and PFA at a thickness of 20 μm as a release layer Is used. The structure of the endless belt 83 is not limited to this. For example, the endless belt 83 is a synthetic material having excellent heat resistance and releasability as a release layer on the surface of a base material made of a heat-resistant resin other than polyimide or a metal material such as stainless steel or nickel. It is good also as a 2 layer structure which formed the resin material (For example, fluororesins, such as PFA and PTFE). In order to reduce the shifting force of the endless belt 83 (the force acting on the endless belt 83 in the direction perpendicular to the rotation direction), the inner surface of the belt base material may be coated with a fluorine resin or the like, Protruding portions (beads) for regulating the biasing force may be provided at both ends of the endless belt 83. In the present embodiment, collars made of heat-resistant resin are applied to both ends of the endless belt 83 to disperse the shifting force, and buckling of the endless belt 83 is reduced.

  The heating rollers 81 and 82 are made of a hollow cylindrical metal core made of aluminum or iron-based material. In order to reduce the shifting force of the endless belt 83, the surface of the metal core material may be coated with a fluororesin or the like. In this embodiment, the heating rollers 81 and 82 are made by coating the surface of an aluminum cored bar having a thickness of 0.75 mm with a fluorine resin blended with PTFE and PFA at a thickness of 20 μm.

  Thermistors 65, 75, and 85 as temperature detecting means are disposed on the peripheral surfaces of the fixing roller 60, the pressure roller 70, and the endless belt 83 so as to detect the respective surface temperatures. . Then, based on the temperature data detected by each thermistor, each heater lamp is controlled so that the control device 90 as a control means maintains the temperatures of the fixing roller 60, the pressure roller 70, and the endless belt 83 at a predetermined temperature. Controls the supply power (energization) to In the present embodiment, the thermistor 65 is divided into two thermistors (not shown) that detect the temperatures at the center and end of the fixing roller 60. Contact thermistors are used to detect temperatures at one end of the fixing roller 60, one end of the pressure roller 70, and the center of the endless belt 83, respectively. In order to detect the temperature, a non-contact temperature sensor is provided. However, the configuration of the temperature detection means is not limited to this. For example, a contact type thermistor may be used, a non-contact type temperature sensor that detects the temperature by detecting infrared rays emitted from the surface may be used, or a contact type and a non-contact type may be mixed. Good.

  Then, the recording paper on which an unfixed toner image is formed at a predetermined fixing speed and copying speed is conveyed to the fixing nip portion N, and fixing is performed by heat and pressure. The fixing speed is a so-called process speed. The copying speed is the number of copies per minute. Although these speeds are not particularly limited, in this embodiment, in monochrome printing, the fixing speed is 355 mm / sec, the copying speed is 70 sheets / min, or the fixing speed is 300 mm / sec, and the copying speed is 62 sheets / min. In color printing, the fixing speed is 220 mm / sec and the copying speed is 50 sheets / min.

  The fixing roller 60 is rotationally driven by a rotational drive device (rotational drive means) 91 including a drive transmission mechanism such as a drive motor and a gear. Further, the pressure roller 70 rotates following the rotation of the fixing roller 60. Accordingly, the fixing roller 60 and the pressure roller 70 are rotated in the opposite directions as shown in FIG. As a result, the recording paper P passes through the fixing nip portion N. In this embodiment, the fixing roller 60 is rotationally driven and the pressure roller 70 is driven to rotate. However, the present invention is not limited to this. For example, the pressure roller 70 is rotationally driven and the fixing roller 60 is driven to rotate. A configuration may be adopted.

  Next, the configuration of the external heating device 80 will be described with reference to FIGS. 3 (a) and 3 (b). FIG. 3A is a cross-sectional view showing a state where the endless belt 83 is in contact with the fixing roller 60, and FIG. 3B is a cross-sectional view showing a state where the endless belt 83 is separated from the fixing roller 60. . In this embodiment, the separation of the endless belt 83 from the fixing roller 60 means that the heating rollers 81 and 82 are moved from the surface of the fixing roller 60 (separated from the fixing roller 60) and are shown in FIG. The endless belt 83 is further away from the fixing roller 60 than the contact state (the state in which the endless belt 83 is heated with the fixing roller 60 and is applied with a first tension that is driven and rotated by the fixing roller 60). This means that the tension acting on the endless belt 83 is changed to a second tension that is weaker than the first tension, and the endless belt 83 does not necessarily have to be completely separated from the fixing roller 60. .

  As shown in FIGS. 3A and 3B, the external heating device 80 includes an endless belt 83, heating rollers 81 and 82, heater lamps 86 and 87, a frame 101, an arm 102, fulcrums 104 and 105, and eccentricity. A cam 103 and a spring 106 are provided.

  The frame 101 is provided on both ends of the heating rollers 81 and 82, and rotatably supports the heating rollers 81 and 82 via bearings (not shown). That is, the heating rollers 81 and 82 are rotatably supported by the frame 101 via bearings (not shown) so as to face each other with a predetermined inter-axis distance. Thereby, the parallelism between the heating rollers 81 and 82 is ensured. In the present embodiment, the parallelism tolerance of the heating rollers 81 and 82 is 100 μm or less. The frame 101 is pivotally supported by the arm 102 at a fulcrum 104 and is rotatable with respect to a direction perpendicular to the axial direction of the heating rollers 81 and 82.

  One end of the arm 102 is supported so as to be rotatable with a fulcrum 105 attached to a frame of the fixing device 1 (not shown) being stopped. The arm 102 is urged by a spring 106 in a direction in contact with the fixing roller 60.

  The eccentric cam 103 is provided so as to contact the other end of the arm 102. The eccentric cam 103 is rotationally driven by a cam driving device 110. The operation of the cam drive device 110 is controlled by the control device 90. As a result, the control device 90 controls the cam driving device 110 to rotate the eccentric cam 103 and move the arm 102 in a direction away from the fixing roller 60 (see FIG. 3B) or in a contact direction. (See FIG. 3A). In conjunction with the movement of the arm 102, the endless belt 83 can be brought into pressure contact with the fixing roller 60 or can be separated by releasing the pressure.

  Next, processing of the control device 90 when the fixing device 1 is warmed up will be described with reference to FIGS. 4 and 5. FIG. 4 is a flowchart showing the flow of processing of the control device 90 during warm-up, and FIG. 5 is a graph showing changes in the surface temperature of the endless belt 83, the fixing roller 60, and the pressure roller 70 during warm-up. . In the present embodiment, the warm-up operation is started from the state where the rotation of the fixing roller 60 is stopped at room temperature until the surface temperatures of the endless belt 83, the fixing roller 60, and the pressure roller 70 reach predetermined target temperatures, respectively. A warm-up operation was performed. Further, in the present embodiment, for the target temperature of each member for warm-up, the target temperature (fourth target temperature T4) at the center of the fixing roller 60 is 195 ° C., and the target temperature at the end of the fixing roller 60 (sixth target temperature). The temperature T6) is 185 ° C., the target temperature at the end of the pressure roller 70 (fifth target temperature T5) is 140 ° C., and the target temperature at the center of the endless belt 83 (third target temperature T3) is 215 ° C. After reaching the temperature, it was idled for 5 seconds to complete the warm-up.

  When warming up, the control device 90 first supplies power to the heater lamps 86 and 87 provided in the heating rollers 81 and 82 of the external heating device 80 and starts heating the endless belt 83 in the external heating device 80. (S1). At this time, the control device 90 supplies heating power (heater lamps 64a, 64b, 74, 86, and 87) that can be used for heating the endless belt 83, the fixing roller 60, and the pressure roller 70 in the fixing device 1. All possible electric power) is supplied to the heater lamps 86 and 87.

  Next, the control device 90 determines whether or not the surface temperature of the endless belt 83, that is, the detected temperature of the thermistor 85 has reached the first target temperature T1 (S2). Here, the first target temperature T1 is preferably set to be equal to or higher than a temperature at which the residual stress (internal stress) in the endless belt 83 is relaxed and equal to or lower than a second target temperature described later. For example, when an endless belt made of a resin such as polyimide is used, the first target temperature T1 is softened by heating the endless belt, the internal stress (residual stress) is relaxed, and the mold attached to the endless belt 83 is relaxed or The temperature to be removed (however, the temperature at which the endless belt does not melt) may be set. Further, when an endless belt made of a metal material such as stainless steel or nickel is used, the internal stress (residual stress) of the endless belt is relaxed at the first target temperature T1, and the mold attached to the endless belt 83 is relaxed or removed. The temperature may be set to a certain temperature. The first target temperature T1 may be set near the standby temperature or slightly lower than the standby temperature. The first target temperature T1 is preferably a high temperature that does not cause thermal damage to the endless belt 83 and peripheral components. In the present embodiment, the first target temperature T1 is 185 ° C.

  If it is determined in S2 that the detected temperature of the thermistor 85 has not reached the first target temperature T1, the control device 90 continues to supply power to the heater lamps 86, 87, and the detected temperature of the thermistor 85 is the first target temperature. It is continuously monitored that the temperature T1 is reached.

  On the other hand, if it is determined in S2 that the detected temperature of the thermistor 85 has reached the first target temperature T1, the control device 90 controls the operation of the cam drive device 110 and changes the tension acting on the endless belt 83. An operation is performed (S3). Here, the tension variation operation is an operation including at least one each of a relaxing operation for reducing the tension of the endless belt 83 and a tension applying operation for increasing the tension at the time of the relaxing operation. That is, in the tension fluctuation operation, at least one cycle for performing the relaxation operation and the tension applying operation is performed. Further, the tension of the endless belt 83 during the relaxation operation is preferably smaller than the tension during image formation (fixing processing) in order to effectively relieve the mold attached to the belt. More preferably, the tension is such that it does not act except for the tension caused by the. In this embodiment, the tension of the endless belt 83 during the tension applying operation is the tension during image formation (the tension when the endless belt 83 is brought into contact with the fixing roller 83). However, the present invention is not limited to this. Absent. The tension of the endless belt 83 during the tension applying operation may be larger than the tension during the relaxing operation in order to effectively relieve the mold attached to the belt, and the endless belt 83 is not damaged or plastically deformed. It is preferable to make it larger.

  Next, the control device 90 determines whether or not the surface temperature of the endless belt 83, that is, the detected temperature of the thermistor 85 has reached the second target temperature T2 (S4). Here, the second target temperature T2 is set to be equal to or higher than the first target temperature T1 and lower than the warm-up target temperature of the endless belt 83. In the present embodiment, the second target temperature T2 is set to 190 ° C.

  Then, when the detected temperature of the thermistor 85 has not reached the second target temperature T2, the control device 90 continues to supply power to the heater lamps 86 and 87, and the detected temperature of the thermistor 85 becomes the second target temperature. Continue monitoring for reaching T2.

  On the other hand, when the detected temperature of the thermistor 85 reaches the second target temperature T2, the control device 90 controls the operation of the rotation driving device 91 to start the rotation of the fixing roller 60 (S5). As a result, heat transfer from the endless belt 83 to the fixing roller 60 is promoted, the temperature of the endless belt 83 decreases as shown in FIG. 5, and the temperatures of the fixing roller 60 and the pressure roller 70 increase. In addition, since the power supply to the heater lamps 86 and 87 is continued, the temperature of the endless belt 83 is once lowered, but is then heated again to rise in temperature.

  Thereafter, the control device 90 monitors that the temperature of the endless belt 83 reaches the third target temperature T3 that is the warm-up target temperature (S6). When the temperature of the endless belt 83 reaches the third target temperature T3, the control device 90 uses the heating power that has been supplied only to the heater lamps 86, 87 of the external heating device 80 until then as the heater lamps 86, 87. And the heater lamp 64a of the fixing roller 60 (S7).

  Thereafter, the control device 90 monitors whether the temperature of the central portion of the fixing roller 60 reaches the fourth target temperature T4 that is the warm-up target temperature (S8). When the temperature of the central portion of the fixing roller 60 reaches the fourth target temperature T4, the control device 90 uses the heating power that has been supplied to the heater lamps 64a, 86, and 87 until then as the heater lamp of the fixing roller 60. 64b, the heater lamp 74 of the pressure roller 70, and the heater lamps 86 and 87 of the external heating device 80 are distributed (S9).

  Thereafter, the control device 90 monitors whether the temperature of the pressure roller 70 reaches the fifth target temperature T5, which is the warm-up target temperature (S10). When the temperature of the pressure roller 70 reaches the fifth target temperature T5, the power supply to the heater lamp 74 of the pressure roller 70 is stopped, and the heating power is supplied to the heater lamp 64b of the fixing roller 60 and the external heating device 80. The heater lamps 86 and 87 are distributed (S11).

  Thereafter, the control device 90 monitors whether the temperature of the end portion of the fixing roller 60 reaches the sixth target temperature T6 that is the warm-up target temperature (S12). When the temperature of the end portion of the fixing roller 60 reaches the sixth target temperature T6, the fixing roller 60 is idled for a predetermined time (in this embodiment, 5 seconds) in this state, and then the warm-up operation is completed.

  Next, the results of an experiment conducted for examining the effect of reducing the rotation failure of the endless belt 83 by the fixing device 1 according to the present embodiment will be described.

(Example)
A warm-up operation was performed from room temperature using an endless belt 83 in which a fixed matter or deposit such as toner was fixed in a film shape over the entire surface. The first target temperature T1 was set to 185 ° C., and when the detected temperature of the endless belt 83 reached 185 ° C., the cam driving device 110 was operated to perform the tension applying operation of the endless belt 83. Here, each of the relaxing operation and the tension applying operation was performed once. Further, the second target temperature T2 was set to 190 ° C., and the rotation of the fixing roller 60 was started when the detected temperature of the endless belt 83 reached 190 ° C. FIG. 6 is a graph showing temperature profiles of the fixing roller 60, the pressure roller 70, and the endless belt 83 in this case.

(Comparative example)
Using the same endless belt 83 as in the above example, the warm-up operation was performed from room temperature. Note that the tension fluctuation operation was not performed, and the rotation of the fixing roller 60 was started when the surface temperature of the endless belt 83 reached 175 ° C. FIG. 7 is a graph showing temperature profiles of the fixing roller 60, the pressure roller 70, and the endless belt 83 in this case.

  As shown in FIG. 6, in the case of the above-described embodiment, when the temperature of the endless belt 83 reaches 190 ° C. and the rotation of the fixing roller 60 is started, the endless belt 83 is immediately driven to rotate without causing a slip or the like. Started. As a result, the temperatures of the fixing roller 60, the pressure roller 70, and the endless belt 83 can be raised smoothly, and the warm-up operation is completed in about 295 seconds from the start of the warm-up operation.

  On the other hand, as shown in FIG. 7, in the comparative example, the rotation of the fixing roller 60 was started when the temperature of the endless belt 83 reached 175 ° C. At that time, the endless belt 83 moved only slightly. Almost did not rotate. After that, even when the temperature of the endless belt 83 reached the warm-up target temperature 220 ° C., the state where the endless belt 83 did not rotate continued, and the endless belt 83 rotated for the first time after about 90 seconds had passed since the start of warm-up. As a result of this rotation, the heat supply from the endless belt 83 to the fixing roller 60 increases, the temperature of the endless belt 83 begins to decrease, and the temperature of the fixing roller 60 increases. Thus, in the comparative example, as a result of the rotation failure of the endless belt 83, it took about 305 seconds from the start of warm-up to the end of warm-up. Thus, if the warm-up spec is within 300 seconds, the spec may be out due to a rotation failure.

  As described above, in the present embodiment, when the warm-up operation of the fixing device 1 is performed, the temperature of the endless belt 83 reaches the first target temperature T1 set to a temperature at which the residual stress of the endless belt 83 is relaxed. When this occurs, the tension of the endless belt 83 is changed. That is, the relaxing operation for relaxing the tension of the endless belt 83 and the tension applying operation for increasing the tension of the endless belt 83 are each performed once or more. As a result, the endless belt 83 is deformed due to fluctuations in the tension of the endless belt 83 heated to a temperature at which the residual stress is relaxed, and the endless belt 83 is deformed due to the restoring force acting upon the restoration, The mold attached to the endless belt 83 can be reduced. As a result, it is possible to suppress the occurrence of a rotation failure such as an increase in driving torque or slip between the endless belt 83 and the fixing roller 60.

  Since the rotation failure of the endless belt 83 can be suppressed, heat can be efficiently supplied from the endless belt 83 to the fixing roller 60 (heated member), and the warm-up time can be shortened. In addition, since heat can be sufficiently supplied during printing (during image forming operation), it is possible to suppress deterioration in image quality due to poor fixing.

  In the example shown in FIG. 3B, the endless belt 83 is in contact with the fixing roller 60 when the tension of the endless belt 83 is weakened (at the time of separation). Any configuration that can change the tension acting on the endless belt 83 is acceptable. For example, a part of the endless belt 83 may be in contact with the fixing roller 60 when the tension of the endless belt 83 is weakened (at the time of separation). In this case, since the moving distance from the contact state of the heating rollers 81 and 82 to the separated state can be shortened, the configuration of the fixing device 1 can be reduced in size. Alternatively, the amount of heat supplied from the endless belt 83 to the fixing roller 60 may be controlled by moving the endless belt 83 to change the contact area between the fixing roller 60 and the endless belt 83.

  In the present embodiment, when the temperature of the endless belt 83 reaches the first target temperature T1, the cycle for performing the relaxing operation and the tension applying operation of the endless belt 83 is performed one or more cycles. The number may be set arbitrarily. However, by increasing the number of cycles, the effect of reducing the mold of the endless belt 83 can be improved. On the other hand, if the number of cycles is increased too much, the power consumption increases due to an increase in warm-up time and a decrease in heat supply efficiency. May be reduced. For this reason, the number of the cycles is preferably 1 or more and 5 or less, more preferably 2 or more and 3 or less.

  In the present embodiment, the first target temperature and the second target temperature are 185 ° C. and 190 ° C., respectively, but are not limited to this, and can be set to different temperatures as appropriate. For example, the first target temperature can be 170 ° C., the second target temperature can be 175 ° C., the first target temperature can be 170 ° C., and the second target temperature can be 180 ° C.

[Embodiment 2]
Another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In the first embodiment, when the temperature of the endless belt 83 reaches the first target temperature T1 after starting the warm-up operation, the cam driving device 110 is operated to perform the tension fluctuation operation of the endless belt 83. In the present embodiment, in addition to this, after the rotation of the fixing roller 60 is started, even when the endless belt 83 does not rotate appropriately, the tension variation operation of the endless belt 83 is performed. That is, in this embodiment, the control device 90 has a function as a rotation state determination unit that determines the rotation state of the endless belt 83. After the rotation of the fixing roller 60 is started, the endless belt 83 is appropriately set. When the driven rotation does not occur, the tension variation operation of the endless belt 83 is performed.

  Specifically, the control device 90 monitors the temperature detection result of the endless belt 83 by the thermistor 85 and determines whether or not the endless belt 83 is appropriately driven and rotated by the fixing roller 60 based on the temperature change state. To do.

  FIG. 8 is an explanatory diagram for explaining a method for determining the rotation state of the endless belt 83 by the control device 90. Note that the solid line shown in this figure indicates a state in which the endless belt 83 is appropriately driven and rotated by the fixing roller 60, and the dotted line indicates a state in which the endless belt 83 is driven and rotated while slipping with the fixing roller 60 ( The broken line indicates a state where the endless belt 83 is not rotating due to a rotation failure.

  As shown in this figure, in this embodiment, when the temperature of the endless belt 83 reaches the first target temperature T1, the cam driving device 110 is operated, and then the temperature of the endless belt 83 reaches the second target temperature T2. When it reaches, the rotation of the fixing roller 60 is started. At this time, when the endless belt 83 is appropriately driven and rotated by the fixing roller 60, the amount of heat supplied from the endless belt 83 to the fixing roller 60 increases and the temperature of the endless belt 83 temporarily decreases. Thereafter, the endless belt 83 sequentially supplies the heat amount continuously supplied to the fixing roller 60 via the heating rollers 81 and 82. As a result, the temperature of the endless belt 83 is once lowered by the start of rotation, and then the temperature rises although the rate of temperature increase is smaller than before the start of rotation.

  On the other hand, when the endless belt 83 does not rotate, the amount of heat supplied to the fixing roller 60 is extremely small. Therefore, the temperature of the endless belt 83 does not decrease, and the temperature rises at substantially the same rate as before the start of rotation. to continue. In addition, when rotating while slipping (when rotating at a speed slower than the original peripheral speed), the temperature of the endless belt 83 is only slightly lower than when appropriately driven and rotated. When not rotating, the temperature of the endless belt 83 does not decrease.

  Therefore, the controller 90 starts the rotation of the fixing roller 60 after the temperature of the endless belt 83 reaches the second target temperature T2, and the temperature of the endless belt 83 becomes higher than the second target temperature T2 within a predetermined time. It is determined whether or not the temperature falls below a threshold value Tth set lower by a predetermined temperature. If the temperature of the endless belt 83 does not fall below the threshold value Tth within a predetermined time, it is determined that a rotation failure has occurred. Conversely, when the temperature of the endless belt 83 falls below the threshold value Tth within a predetermined time, it is determined that the driven rotation is appropriately performed.

  FIG. 9 is a flowchart showing a processing flow of the control device 90 during warm-up, and FIG. 10 is a graph showing changes in the surface temperature of the endless belt 83, the fixing roller 60, and the pressure roller 70 during warm-up. . In the present embodiment, the warm-up operation is started from the state where the rotation of the fixing roller 60 is stopped at room temperature until the surface temperatures of the endless belt 83, the fixing roller 60, and the pressure roller 70 reach predetermined target temperatures, respectively. A warm-up operation was performed.

  When warming up, the control device 90 first supplies power to the heater lamps 86 and 87 provided in the heating rollers 81 and 82 of the external heating device 80 and starts heating the endless belt 83 in the external heating device 80. (S21). At this time, the control device 90 supplies heating power (heater lamps 64a, 64b, 74, 86, and 87) that can be used for heating the endless belt 83, the fixing roller 60, and the pressure roller 70 in the fixing device 1. All possible electric power) is supplied to the heater lamps 86 and 87.

  Next, the control device 90 determines whether the surface temperature of the endless belt 83, that is, the detected temperature of the thermistor 85 has reached the first target temperature T1 (S22).

  If it is determined in S2 that the detected temperature of the thermistor 85 has not reached the first target temperature T1, the control device 90 continues to supply power to the heater lamps 86, 87, and the detected temperature of the thermistor 85 is the first target temperature. It is continuously monitored that the temperature T1 is reached.

  On the other hand, if it is determined in S22 that the detected temperature of the thermistor 85 has reached the first target temperature T1, the control device 90 controls the operation of the cam drive device 110 to change the tension acting on the endless belt 83. An operation is performed (S23).

  Next, the control device 90 determines whether the surface temperature of the endless belt 83, that is, the detected temperature of the thermistor 85 has reached the second target temperature T2 (S24).

  Then, when the detected temperature of the thermistor 85 has not reached the second target temperature T2, the control device 90 continues to supply power to the heater lamps 86 and 87, and the detected temperature of the thermistor 85 becomes the second target temperature. Continue monitoring for reaching T2.

  When the detected temperature of the thermistor 85 reaches the second target temperature T2, the control device 90 controls the operation of the rotation drive device 91 to start the rotation of the fixing roller 60 (S25).

  Further, the control device 90 determines whether or not the endless belt 83 is appropriately driven and rotated by the fixing roller 60 by the method described above (S26). If it is determined that the driven rotation is not properly performed, the control device 90 controls the operation of the cam drive device 110 to perform a tension fluctuation operation (S27).

  Thereafter, the control device 90 determines whether or not the temperature of the endless belt 83 has reached the third target temperature T3 (S28). If it is determined that it has not been reached, the processing from S26 is performed again.

  On the other hand, if it is determined that it has reached, the control device 90 determines whether or not the endless belt 83 is appropriately driven and rotated by the fixing roller 60 (S29). If it is determined that the driven rotation is not properly performed, the control device 90 controls the operation of the cam drive device 110 to perform a tension fluctuation operation (S30). On the other hand, when it is determined that the driven rotation is appropriately performed in S29, and after the tension fluctuation operation is performed in S30, the control device 90 has supplied only to the heater lamps 86 and 87 of the external heating device 80 until then. The heating power is distributed to the heater lamps 86 and 87 and the heater lamp 64a of the fixing roller 60 (S31). Note that if it is confirmed in S26 that the endless belt 83 is appropriately driven and rotated, the processes in S29 and S30 may be omitted.

  Thereafter, the control device 90 determines whether or not the temperature of the central portion of the fixing roller 60 has reached the fourth target temperature T4 that is the warm-up target temperature (S32). Then, when the fourth target temperature T4 has not been reached, the processes after S29 are performed again. On the other hand, when the fourth target temperature T4 is reached, the control device 90 uses the heating power that has been supplied only to the heater lamps 64a, 86, 87 until the heater lamp 64b of the fixing roller 60 and the pressure roller 70 are heated. The heater lamp 74 and the heater lamps 86 and 87 of the external heating device 80 are distributed (S33).

  Thereafter, the control device 90 monitors whether the temperature of the pressure roller 70 reaches the fifth target temperature T5, which is the warm-up target temperature (S34). When the temperature of the pressure roller 70 reaches the fifth target temperature T5, the power supply to the heater lamp 74 of the pressure roller 70 is stopped, and the heating power is supplied to the heater lamp 64b of the fixing roller 60 and the external heating device 80. The heater lamps 86 and 87 are distributed (S35).

  Thereafter, the control device 90 monitors whether the temperature of the end portion of the fixing roller 60 reaches the sixth target temperature T6 that is the warm-up target temperature (S36). When the temperature of the end portion of the fixing roller 60 reaches the sixth target temperature T6, the fixing roller 60 is idled for a predetermined time (in this embodiment, 5 seconds) in this state, and then the warm-up operation is completed.

  As described above, in this embodiment, after the rotation of the fixing roller 60 is started, the control device 90 determines whether or not the endless belt 83 is appropriately driven to rotate. When the driven rotation is not properly performed, the cam driving device 110 is operated to perform the tension fluctuation operation of the endless belt 83.

  As a result, the mold attached to the endless belt 83 is reduced, and it is possible to suppress the occurrence of rotation failure such as an increase in driving torque or slip between the fixing roller 60 and the like.

  Further, as the fixing roller 60 and the endless belt 83 rotate, the contact area of the endless belt 83 and the fixing roller 60 with the other member changes, so that there are fixed matters and deposits such as toner on these members. Even in this case, it is possible to prevent a rotation failure such as a slip caused by these fixed matter and deposit.

  Note that the method for determining whether or not the endless belt 83 has a rotation failure is not limited to the method described above, and any method that can appropriately determine the rotation state of the endless belt 83 (the presence or absence of rotation failure) may be used. For example, when the rotation state is determined based on the temperature change of the endless belt 83, the temperature change of the endless belt 83 after the rotation of the fixing roller 60 is detected, and when the temperature rise rate and the temperature drop starts to rise. It may be determined using a bottom value of the temperature or another index related to temperature rise / fall as a parameter.

  The threshold value Tth can be set as appropriate depending on the configuration of various rollers and belts, the configuration of the heater lamp, and the like. Further, when distinguishing between the case of not rotating and the rotation in the slip state, it is possible to set the threshold value Tth1 when not rotating to 188 ° C. and the threshold value Tth2 when rotating while slipping to 183 ° C. It is. That is, if the temperature does not drop below the threshold Tth1 after the rotation of the fixing roller 60, it is determined that the “endless belt is not rotating”. If the temperature is lower than the threshold Tth1 and higher than the threshold Tth2, “the endless belt slips”. If the temperature drops below the threshold value Tth2, it is determined that the driven rotation is appropriate.

  Further, the determination is not limited to the method based on the temperature detection result of the endless belt 83, but may be determined based on the temperature detection result of the fixing roller 60 or the pressure roller 70. When the endless belt 83 is appropriately driven to rotate, the amount of heat supplied from the endless belt 83 to the fixing roller 60 increases, so the temperatures of the fixing roller 60 and the pressure roller rapidly increase. On the other hand, if the endless belt 83 does not rotate properly, the amount of heat supplied to the fixing roller 60 decreases, so that the rate of change in temperature of the fixing roller 60 and the pressure roller 70 decreases. Therefore, the rotational state of the endless belt 83 may be determined based on the temperature change of the fixing roller 60 or the pressure roller 70. Alternatively, the determination may be made based on two or more temperature detection results of the endless belt 83, the fixing roller 60, and the pressure roller 70. Further, the determination may be made using a difference from a predetermined reference temperature or other temperature information, or may be made using the temperature change rate or the difference temperature of both the central portion and the end portion of the fixing roller 60. .

  In this embodiment, the temperature information is used to determine the rotation state of the endless belt 83. However, the present invention is not limited to this, and other methods may be used. For example, the rotation state may be determined by optically detecting a change in state such as irregularities, holes, notches, colors and patterns provided on the external heating belt. Further, the rotation state may be determined by detecting irregularities, holes, notches, and the like provided on the external heating belt by a mechanical method. Alternatively, the rotational state may be determined by capturing a change in magnetic information or a magnetic pattern applied to the endless belt 83.

  In the present embodiment, as in the first embodiment, when the temperature of the endless belt 83 reaches the first target temperature T1, the cam driving device 110 is operated to perform the tension fluctuation operation of the endless belt 83. This is not a limitation. For example, the tension fluctuation operation may be performed only when the endless belt 83 does not rotate properly after the rotation operation of the fixing roller 60 is started.

[Embodiment 3]
Still another embodiment of the present invention will be described. For convenience of explanation, members having the same functions as those in the first and second embodiments are denoted by the same reference numerals, and description thereof is omitted.

  For example, when the image forming apparatus is once started and the warm-up operation is performed, and then restarted from a state in which the image forming apparatus transitions to the standby state, the warm-up operation is performed again. In such a case, if it can be determined that the endless belt 83 can be appropriately driven and rotated by the fixing roller 60 by the warm-up operation when it is first started, it is unlikely that the endless belt 83 has a mold at the time of restart. There is no fear of rotation failure due to the mold, and it is considered that there is no need to perform a tension fluctuation operation.

  Therefore, in this embodiment, when the warm-up operation is once completed and then the warm-up operation is performed again, the fluctuation in the tension of the endless belt 83 is less likely to cause rotation failure due to the mold attached to the endless belt 83. The operation is omitted. Specifically, when the surface temperature of the endless belt 83 reaches the first target temperature T1 after the warm-up is started and the surface temperature of the central portion of the fixing roller 60 is 100 ° C. or higher, the tension fluctuation operation is omitted. To do.

  FIG. 11 is a flowchart showing a processing flow of the control device 90 during warm-up, and FIG. 12 is a graph showing changes in the surface temperature of the endless belt 83, the fixing roller 60, and the pressure roller 70 during warm-up. .

  When warming up, the control device 90 first supplies power to the heater lamps 86 and 87 provided in the heating rollers 81 and 82 of the external heating device 80 and starts heating the endless belt 83 in the external heating device 80. (S41). At this time, the control device 90 supplies heating power (heater lamps 64a, 64b, 74, 86, and 87) that can be used for heating the endless belt 83, the fixing roller 60, and the pressure roller 70 in the fixing device 1. All possible electric power) is supplied to the heater lamps 86 and 87.

  Next, the control device 90 determines whether or not the surface temperature of the endless belt 83, that is, the detected temperature of the thermistor 85 has reached the first target temperature T1 (S42).

  If it is determined in S42 that the detected temperature of the thermistor 85 has not reached the first target temperature T1, the control device 90 continues to supply power to the heater lamps 86 and 87, and the detected temperature of the thermistor 85 is the first target temperature. It is continuously monitored that the temperature T1 is reached.

  On the other hand, if it is determined in S42 that the temperature detected by the thermistor 85 has reached the first target temperature T1, the controller 90 determines whether the temperature at the center of the fixing roller 60 is equal to or higher than a predetermined temperature (100 ° C. in this case) T8. It is determined whether or not (S43). When the temperature of the central portion of the fixing roller 60 is lower than the predetermined temperature T8, the control device 90 controls the operation of the cam driving device 110 to perform a tension changing operation for changing the tension acting on the endless belt 83 ( S44).

  Then, after performing the tension fluctuation operation in S44, and when it is determined in S43 that the temperature of the central portion of the fixing roller 60 is equal to or higher than the predetermined temperature T8, the control device 90 performs the processes of S45 to S53. Note that the processing of S45 to S53 is the same as the processing of S4 to S12 in FIG. 4 described in the first embodiment, and thus the description thereof is omitted here.

  As described above, in this embodiment, after the warm-up operation is started, when the temperature of the endless belt 83 reaches the first target temperature T1, the control device 90 sets the temperature of the center portion of the fixing roller 60 to a predetermined temperature. It is determined whether this is the case. When the temperature is equal to or higher than the predetermined temperature, the tension fluctuation operation of the endless belt 83 is omitted.

  Thereby, when there is a low possibility that the endless belt 83 has a mold, it is possible to shorten the warm-up time by omitting the tension fluctuation operation.

  In the present embodiment, whether or not the temperature of the central portion of the fixing roller 60 is equal to or higher than a predetermined temperature (100 ° C. in the present embodiment) is used as a criterion for determining whether or not the tension changing operation is necessary, but the criterion is limited to this. Any standard may be used as long as it can be determined whether there is a possibility that rotation failure may occur due to the mold attached to the endless belt 83. For example, the predetermined temperature may be set to a temperature different from 100 ° C. (for example, 120 ° C., 150 ° C., 80 ° C., etc.) according to the configuration of the fixing device 1.

  Further, the determination is not limited to the configuration based on the temperature at the center of the fixing roller 60, but the temperature at the end of the fixing roller 60, the temperature of the pressure roller 70, the temperature of the heating rollers 81 and 82, or the temperature of a plurality of members. You may judge combining conditions.

  In addition, the operation condition of the fixing device 1, the sheet passing conditions such as the number of recording sheets to be passed or the number of sheets to be passed, the difference information between the detected temperature of each member provided in the fixing device 1 and the target temperature may be used as the determination criteria. . Further, the control device 90 measures the elapsed time since the previous warm-up operation or image forming operation, or the elapsed time after the temperature of the endless belt 83 drops below a predetermined temperature, and the time measurement result is obtained. Based on this, the necessity of the tension applying operation may be determined.

  Further, when the warm-up operation has already been performed and the rotation state of the endless belt 83 is being performed, the temperature state of the fixing roller 60 or the endless belt 83 is stored in a memory or the like, and then the warm-up operation is performed. The necessity of the tension applying operation may be determined by comparing the temperatures of the fixing roller 60 and the endless belt 83.

  Also, whether to return from the low-power mode, whether to return from paper jam during printing, the number of prints made so far, the remaining number of prints and the total number of prints, paper type, environmental conditions, image formation The determination may be made using various parameters indicating the operation conditions of the fixing operation such as the operation time of the apparatus or the fixing device.

  Further, in each of the above embodiments, the tension fluctuation operation of the endless belt 83 is performed in the period from the start of the warm-up to the completion of the warm-up, but not limited thereto, for example, after completing the warm-up, The tension fluctuation operation may be performed during a period until the recording paper is conveyed to the fixing nip portion. Thereby, it is possible to appropriately supply heat from the endless belt 83 to the fixing roller 60 during the image forming operation.

  For example, the control device 90 is configured to determine the rotation state of the endless belt 83 in the same manner as in the second embodiment, and it is not possible to confirm that the endless belt 83 is appropriately driven and rotated during the warm-up period. Alternatively, the tension fluctuation operation may be performed during a period after the warm-up is completed and before the recording sheet is conveyed to the fixing nip portion.

  Further, for example, when the endless belt 83 does not appropriately rotate after the warm-up operation is completed, the fixing roller 60 is stopped in the print standby state until the first recording sheet is passed. The tension variation operation of the endless belt 83 may be performed every predetermined time interval (for example, every 2 minutes). In this case, the process of performing the tension fluctuation operation at every predetermined time interval may be performed during a period until a predetermined time (for example, 10 minutes) elapses after the warm-up is completed. In addition, the number of times of the relaxing operation and the tension applying operation in the tension changing operation performed every predetermined time interval may be set arbitrarily.

  Further, the number of operations of the cam drive device 110 (number of times of performing the relaxation operation and the tension applying operation) and the operation conditions are changed based on the various parameters described above (temperature conditions, elapsed time, operation conditions, etc. of each member). May be.

  In each of the above embodiments, the configuration in which the tension of the endless belt 83 is changed by controlling the operation of the cam driving device 110 to bring the endless belt 83 into contact with or away from the fixing roller 60 has been described. However, the present invention is not limited to this, and it is only necessary to include tension changing means that can change the tension of the endless belt 83. For example, a tension roller (not shown) is provided as a member for stretching the endless belt 83 in addition to the heating rollers 81 and 82, and the tension of the endless belt 83 can be changed by moving the position of the tension roller. Good. Further, a pad-like member may be provided instead of the tension roller. Further, the tension of the endless belt 83 may be changed by changing the distance between the axes of the heating rollers 81 and 82. Further, the tension of the endless belt 83 may be changed by moving the relative position of the fixing roller 60 with respect to the heating rollers 81 and 82.

  In each of the above embodiments, the heater lamps are provided in the fixing roller 60 and the pressure roller 70, respectively, but the present invention is not limited to this. For example, the pressure roller 70 may not be provided with a heater lamp. Further, the fixing roller 60 and the pressure roller 70 may not be provided with a heater lamp.

  Moreover, in each said embodiment, although the endless belt 83 is heated with the heater lamps 86 and 87 with which the inside of the heating rollers 81 and 82 was equipped, not only this but heating from the surface of the endless belt 83, The endless belt 83 itself may be configured to generate heat, and it is only necessary to include a heating unit that can heat the endless belt 83 to a predetermined temperature.

  In each of the above embodiments, the control device 90 is configured from the control integrated circuit board. However, the control device 90 is not limited thereto, and may be realized by software using a processor such as a CPU. In this case, for example, the control device 90 includes a CPU (central processing unit) that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, and a RAM (random access) that expands the program. memory), a storage device (recording medium) such as a memory for storing the program and various data. An object of the present invention is to provide a recording medium in which a program code (execution format program, intermediate code program, source program) of a control program of the control device 90, which is software that realizes the functions described above, is recorded in a computer-readable manner The program is supplied to the control device 90, and the computer (or CPU or MPU) reads and executes the program code recorded on the recording medium.

  Examples of the recording medium include a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a floppy (registered trademark) disk / hard disk, and an optical disk such as a CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

  The control device may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. This communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, A satellite communication network or the like can be used. Further, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE1394, USB, power line carrier, cable TV line, telephone line, ADSL line, infrared rays such as IrDA and remote control, It is also possible to use wireless such as Bluetooth (registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network. The present invention can also be realized in the form of a computer data signal (data signal sequence) embedded in a carrier wave in which the program code is embodied by electronic transmission.

  In this embodiment, the case where the present invention is applied to a color image forming apparatus has been described. However, the present invention is not limited to this, and the present invention can also be applied to an image forming apparatus that forms a monochrome image (monochromatic image).

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and the embodiments can be obtained by appropriately combining the respective technical means disclosed in the above-described embodiments. The form is also included in the technical scope of the present invention.

  The present invention can be applied to an external belt heat fixing type fixing device and an image forming apparatus including the same.

1 is a schematic diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a schematic configuration of a color image forming apparatus (image forming apparatus) according to an embodiment of the present invention. 2A is a cross-sectional view showing a state in which the endless belt is brought into contact with the fixing roller in the fixing device shown in FIG. 1, and FIG. It is sectional drawing which shows the state. FIG. 2 is a flowchart showing a flow of processing during warm-up in the fixing device shown in FIG. 1. 2 is a graph showing changes in surface temperatures of an endless belt, a fixing roller, and a pressure roller during warm-up in the fixing device shown in FIG. 1. 2 is a graph showing changes in surface temperatures of an endless belt, a fixing roller, and a pressure roller during warm-up when the control method of the present invention is applied to the fixing device shown in FIG. 1. 2 is a graph showing changes in surface temperatures of an endless belt, a fixing roller, and a pressure roller during warm-up when a conventional control method is applied in the fixing device shown in FIG. 1. It is explanatory drawing which shows the determination method of the rotation state of an endless belt in the fixing device concerning other embodiment of this invention. FIG. 9 is a flowchart showing a flow of processing during warm-up in a fixing device according to another embodiment of the present invention. 6 is a graph showing changes in surface temperatures of an endless belt, a fixing roller, and a pressure roller during warm-up in a fixing device according to another embodiment of the present invention. FIG. 10 is a flowchart showing a flow of processing during warm-up in a fixing device according to still another embodiment of the present invention. 6 is a graph showing changes in surface temperatures of an endless belt, a fixing roller, and a pressure roller during warm-up in a fixing device according to still another embodiment of the present invention.

Explanation of symbols

1 Fixing device 60 Fixing roller (fixing member)
64a, 64b heater lamp 65 thermistor (second temperature detecting means)
70 Pressure roller (Pressure member)
74 Heater lamp 75 Thermistor (third temperature detection means)
80 External heating device 81, 82 Heating roller (supporting member)
83 Endless belt (belt)
85 Thermistor (first temperature detection means)
86,87 Heater lamp (heating means)
90 Control device (control means)
91 Rotation drive device (rotation drive means)
101 frame (tension fluctuation means)
102 Arm (Tension variation means)
103 Eccentric cam (Tension fluctuation means)
104, 105 fulcrum 106 spring (tension variation means)
110 Cam drive device (tension fluctuation means)

Claims (12)

A fixing member and a pressure member that contact each other with a predetermined load; and a rotation driving unit that rotates at least one of the fixing member and the pressure member to rotate the fixing member and the pressure member; An external heating device that heats the belt stretched by a plurality of support members by heating means and abuts against the peripheral surface of the fixing member to heat the fixing member and to rotate the belt following the fixing member; An unfixed image on the recording material is conveyed by conveying the recording material carried into a contact portion between the fixing member and the pressure member while being sandwiched between the fixing member and the pressure member. A fixing device for fixing to the recording material by heat of a peripheral surface of a fixing member,
Tension changing means for performing a tension changing operation including at least one of a relaxing operation for reducing the tension of the belt and a tension applying operation for increasing the tension of the belt more than a tension at the time of the relaxing operation;
Control means for controlling the operation of the tension fluctuation means,
The control means includes
After the heating of the belt is started by the heating means, before the recording material is carried between the fixing member and the pressure member, the tension changing means performs the tension changing operation. Fixing device to do. The rotational driving operation by the rotational driving means is performed after the start of heating of the belt,
The control means includes
2. The tension changing unit according to claim 1, wherein after the heating unit starts heating the belt, the tension changing unit performs the tension changing operation before starting the rotation driving operation by the rotation driving unit. Fixing device. First temperature detecting means for detecting the temperature of the belt,
The control means includes
Causing the tension changing means to perform the tension changing operation when the temperature detected by the belt by the first temperature detecting means reaches a first temperature that is set to be equal to or higher than a temperature at which the residual stress of the belt starts to be relieved. The fixing device according to claim 1, wherein: The control means includes
When the temperature detected by the belt by the first temperature detecting means reaches a second temperature set to a temperature higher than the first temperature, the rotational driving operation by the rotational driving means is started. The fixing device according to claim 3.   The control means determines whether or not rotation failure has occurred in the belt after starting the rotation drive operation by the rotation drive means, and when the rotation failure has occurred, the tension fluctuation means causes the tension fluctuation change to occur. The fixing device according to claim 1, wherein an operation is performed. The control means includes
The detected temperature of the belt by the first temperature detecting means does not fall below a threshold temperature set to a temperature lower than the second temperature within a predetermined time after starting the rotational driving operation by the rotational driving means. The fixing device according to claim 4, wherein the tension changing unit causes the tension changing unit to perform the tension changing operation. A fixing member and a pressure member that contact each other with a predetermined load; and a rotation driving unit that rotates at least one of the fixing member and the pressure member to rotate the fixing member and the pressure member; An external heating device that heats the belt stretched by a plurality of support members by heating means and abuts against the peripheral surface of the fixing member to heat the fixing member and to rotate the belt following the fixing member; An unfixed image on the recording material is conveyed by holding the recording material carried into the contact portion between the fixing member and the pressure member while being sandwiched between the fixing member and the pressure member. A fixing device that fixes the recording material with heat of the peripheral surface of the fixing member,
Tension changing means for performing a tension changing operation including at least one of a relaxing operation for reducing the tension of the belt and a tension applying operation for increasing the tension of the belt more than a tension at the time of the relaxing operation;
Control means for controlling the operation of the tension fluctuation means;
The temperature of at least one of the first temperature detecting means for detecting the temperature of the belt, the second detecting means for detecting the temperature of the fixing member, and the third temperature detecting means for detecting the temperature of the pressure member. Detecting means,
The control means includes
Only when the temperature detected by each temperature detecting means is lower than a predetermined temperature preset for each temperature detecting means, the heating means starts heating the belt, and then the rotational driving operation by the rotational driving means. A fixing device that causes the tension changing means to perform the tension changing operation before starting the operation.   The fixing device according to claim 1, wherein the control unit causes the relaxation operation and the tension applying operation to be performed a plurality of times as the tension fluctuation operation.   An image forming apparatus comprising the fixing device according to claim 1. A fixing member and a pressure member that contact each other with a predetermined load; and a rotation driving unit that rotates at least one of the fixing member and the pressure member to rotate the fixing member and the pressure member; An external heating device that heats the belt stretched by a plurality of support members by heating means and abuts against the peripheral surface of the fixing member to heat the fixing member and to rotate the belt following the fixing member; An unfixed image on the recording material is conveyed by conveying the recording material carried into a contact portion between the fixing member and the pressure member while being sandwiched between the fixing member and the pressure member. A control method of a fixing device for fixing to a recording material by heat of a peripheral surface of a fixing member,
The fixing device includes a tension changing unit that performs a tension changing operation including at least one of a relaxing operation for reducing the tension of the belt and a tension applying operation for increasing the tension of the belt more than a tension at the time of the relaxing operation. Has
Including a step of causing the tension changing means to perform the tension changing operation after the heating means starts heating the belt and before the recording material is carried between the fixing member and the pressure member. A control method for a fixing device.   A program for operating the fixing device according to any one of claims 1 to 8, wherein the program causes a computer to function as the control unit.   The computer-readable recording medium which recorded the program of Claim 11.

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